An osteotomy is a surgical procedure for straightening bones wherein the bone is cut transversely and a corrective segment having a tapered or wedge shape is removed from the outside of an undesired bend in the bone. After the corrective segment has been removed the bone segments are brought together to close the wedge-shaped gap left by the removed segment, thereby straightening the bone, which knits in the new orientation. In an arcuate osteotomy, rather than removing a corrective segment across the entire width of the bone, the correction extends only partially across the width of the bone, to an arcuate cut which extends across the rest of the width of the bone. The correction is wider (in the direction longitudinally of the bone) than the kerf of the arcuate cut, and its width and taper determine the amount of correction or straightening. Removal of the correction leaves a gap to one side of the pivot; the opposite bone segments are repositioned around the arcuate cut to close the correction gap and thereby straighten the bone. The technique provides cuts with comparatively long abutting areas, which improves bone knitting. Further discussion of the arcuate osteotomy technique is set forth in my prior U.S. Pat. No. 4,501,268, issued Feb. 26, 1985, to which reference may be had.
My patent application Ser. No. 07/308,257, previously referred to, in a preferred embodiment discloses a technique wherein the arcuate cut is made with a semicircularly curved saw blade. The blade has saw teeth along a longitudinal edge, parallel to its axis of curvature. The blade is guided to cut the desired arc in the bone by a guide having a curved slot along which the blade is advanced, the curved cross-sectional shape of the blade helping the blade to track in its own kerf. Once the arcuate cut has been made, the correction is then cut in three steps. A first correction cut, which will define one side of the wedge-shaped correction, is made from the opposite bone side to the inner end of the arc, but only partially through the thickness of the bone so that the bone is not altogether severed. Using the first correction cut as a guide, a second correction cut is then made at a desired longitudinal spacing from it. This second cut is made through the entire thickness of the bone, thereby severing the bone into two segments. The two correction cuts define a tapered wedge between them which extends from the side of the bone to the arcuate cut. In the third step the first correction cut is then completed through the thickness of the bone, thereby freeing the wedge which is removed. The two bone segments are articulated about the arc to close the gap and straighten the bone. The reason for making the first correction cut through only a part of the thickness of the bone is that if it were cut through the entire thickness, the bone would be severed before the second correction cut had been made, which would make it more difficult to properly position and make the second correction cut. By making the first cut only partial, it can be used as a guide to more precisely position the second cut.
It can be seen that the arcuate technique described is relatively complicated in that it requires three separate steps to define and remove the wedge: the incomplete first correction cut, the second correction cut, and a third cut along the line of the first cut to free the correction wedge.